Electron tube



M. KNOLL ELECTRON TUBE July 13, 1937.

Filed Feb. 9, 1935 [XIERAAL I INVENTOR mx mom BY ATII'ORNEY Patented July 13,, 1937 UNITED STATES 2,086,718 ELECTRON TUBE Max Knoll, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application February 9, 1935, Serial No. 5,703 In Germany January 27, 1934 1 Claim.

This invention relates in general to electron tubes and particularly to electron tubes of the cathode ray type comprising one or more fluorescent screens.

In cathode ray tubes the problem frequently arises to produce a fluorescent spot of extremely great luminous density combined with a very reduced diameter, for example, of the order of 1 mm. However, this is feasible only to a certain limit seeing that the heating of the fluorescent substance becomes so intense as soon as a certain critical density of electrons is attained that the luminosity thereof decreases if the current density is further raised. This situation holds good especially in connection with fluorescent screens of the type in which the fluorescent material has been applied upon a glass support or substratum.

In order to obviate this difliculty, the suggestion has been made in the earlier art to use fluorescent screens with a metallic sup-port for the active material. However, quite apart from the fact that this solution is no longer useful when the screen has to be viewed from the posterior side, a certain limitation is imposed also in this case at which the admissible heating of the fluorescent substance will be exceeded and where a further rise in luminosity is no longer feasible.

The present invention is concerned with cathode ray tubes in which the density of electron current impinging upon a unit of surface or area inside a unit of time is very high, and its aim is to insure a further increase of the fluorescence luminosity beyond the limits above outlined. This is particularly important in the case of cathode ray tubes in which the electron spot impinges always upon the same place of the fluorescent screen and where the spot, therefore, is not subject to electrical or magnetic deflection by fields acting upon the path of the pencil. Tubes of this kind are used, for instance, in sound film work.

The invention is valuable also in cases where a deflection of the spot is produced in one or in more directions, especially where large electron currents and voltages are employed, and where the tube is severed from the pump permanently so that no substitution of the fluorescent screen is possible.

According to the invention the suggestion is made to make the fluorescent screen pivotal in the zone of deflection of the electron spot in such a way that when turning the fluorescent screen, the sharpness or focus of the electron spot is preserved. Such rotation or pivoting may be either intermittent, which could be accomplished by the agency of an auxiliary magnet mounted outside the tube coacting with an iron core attached to the fluorescent screen, or else it may be made continuous in that upon the pivoting axis of the screen placed inside a vacuous space a keeper is 5 attached which is adapted to be set into rotation conjointly with the said screen by the aid of a rotary magnetic field provided outside the tube.

Two embodiments of the basic idea of the invention are illustrated in the drawing covering 10 the case of continuous motion of the fluorescent screen:

Fig. 1 showing a cathode ray tube for sound film work with a rotary fluorescent screen brought upon a glass support according to this 15 invention; while Fig. 2 illustrates a television tube comprising a rotatable fluorescent screen comp-rising a metal support according to this invention.

Referring to the drawing and first to Fig. 1, L 2() denotes a coat of fluorescent material which has been placed upon a flat glass pane G. The latter is disposed in the interior of a severed and sealed cathode ray tube T in away so as to be pivotal about the axis A. The rotation is insured by the aid of an eddy current motor whose stator and rotor are designated by S and B, respectively. The pencil OR of cathode rays developed within the tube structure and directed toward the screen L through the electron gun'structure comprising a cathode and anode as well as any desired control electrodes, herein gene-rally designated GS; is so directed as to impinge upon the spot P and excite fluorescent effects on the screen L. The light issuing from the luminous spot P is suitably limited by the aid of a diaphragm B, and it is caused to fall upon the film F upon which a record is to be formed either directly or by way of lenses or the like.

Referring to Fig. 2, legend G1 denotes a roa0 tatably disposed metallic disk confined inside a cathode ray tube upon which a fluorescent substance as indicated at L is applied in any desired manner. Owing to the rotation of the disk G1, it is feasible to generate an extremely intense spot upon the fluorescent substance L. The electron beam or cathode ray CR is moved over the rotating screen surface L by the agency of suitable electromagnetic deflecting coils M (or, where desired, electrostatic fields). The resulting light spot is imaged by the aid of an optical system 0 upon the film F posteriorly of which latter there is mounted a photoelectric cell Z. The substance of the fluorescent screen should have an after glow or phosphorescent effect being suitably small compared with the speed of rotation of the fluorescent screen.

Having now described the invention, what I claim and desire to secure by Letters Patent is the following:

A cathode ray device comprising means to develop an electron beam and to direct the beam through the device along predetermined paths, a rotary transparent disk member positioned transverse to the path of the electron beam, a coating of fluorescent material upon the surface of the disk member nearest the source of the electron beam, said coating being adapted to fiuoresce under the influence of the electron beam during periods of impact, a shaft about which said disc is adapted to rotate and positioned eccentrically to the normal path of the beam and means connected with said shaft to rotate said disk member relative to the electron beam, said means comprising a motor having a rotor disposed within the device and a stator cooperatively associated with the rotor and arranged ex- 10 ternally of the device.

MAX KNOLL. 

